Thin-film-transistor liquid crystal display (LCD) has been extensively used for electronic appliances. The LCD panel is composed of a plurality of liquid crystal (LC) cells, arranged in a row-column matrix manner, each cell having an individual signal electrode forming a cell capacitor with a common electrode shared by other cells. To prevent LC polarization that causes image residue and LC damage, LC cells are required to be driven by alternating polarity electric field in order to maintain zero DC balance across the LC, whereby voltage polarity applied to each LC cell is inverted on alternate frames. That is, for each LC cell, if its voltage polarity, which is determined by the voltage of its signal electrode with respect to the common electrode (COM), is driven positive in a present time frame, the voltage polarity is then driven negative in a next time frame.
To display images on a LCD panel, column driving signals with voltage magnitudes corresponding to image gray level data are applied to signal electrodes of LC cells on a row by row manner for each image frame under scan driving control method. The necessity for maintaining zero DC balance in the LC cells can readily be achieved by the classic frame inversion scan driving method for LCD panel, whereby all LC cells on each row are driven by driving signals with same voltage polarity, scanning from row to row, for all rows for a frame, and then with opposite or inverted voltage polarity for the next frame. This frame inversion scheme of scan driving method works well for small panel size, but image crosstalk and flicker problems become visible for high resolution large panels due to inconsistent signal voltages across the LC cells arising from various voltage control difficulties in polarity inversion driving. Other inversion schemes using different polarity patterns for LC cells on a row have been developed to reduce such visible artifacts in the displayed image, including row inversion, column inversion and dot inversion.
FIG. 1 shows voltage polarity pattern for driving LC cells in LCD panel using row inversion. In row inversion, during a frame period, each LC cell on the same row is driven with same voltage polarity which is opposite to voltage polarity for LC cells on adjacent rows, as shown in FIG. 1a. The polarity pattern comprises polarity inversion from row to row, but no polarity inversion on a row going from column to column. Then, in the next frame, voltage polarity for each LC cell is inverted, as shown in FIG. 1b. Visible artifacts in the displayed image are reduced for certain images in comparison to frame inversion.
It is common in LCD practices to refer to voltage polarity change by various names, such as polarity inversion or polarity reversion or reversed polarity or opposite polarity. A polarity pattern represents a configuration of polarity inversions or polarity changes. Varying of polarity pattern is varying of the configuration of polarity inversions or polarity changes in the polarity pattern. For a polarity pattern of matrix format the polarity pattern is commonly described in terms of polarity inversion or change with respect to row or column intervals.
FIG. 2 shows voltage polarity pattern for driving LC cells in LCD panel using column inversion, polarity inversion going from column to column. In column inversion, during a frame period, each LC cell on the same column is driven with same voltage polarity, which is opposite to voltage polarity for LC cells on adjacent columns, as shown in FIG. 2a. The polarity pattern comprises polarity inversion from column to column, but no polarity inversion on a column going from row to row. Then, in the next frame, voltage polarity for each LC cell is inverted, as shown in FIG. 2b. Visible artifacts in the displayed image are reduced for certain images in comparison to row inversion.
FIG. 3 shows voltage polarity pattern for driving LC cells in LCD panel using dot inversion. In dot inversion, during a frame period, each LC cell is driven with voltage polarity which is opposite to voltage polarity for surrounding LC cells, as shown in FIG. 3a. The polarity pattern comprises polarity inversion from column to column and also from row to row. Then, in the next frame, voltage polarity of each LC cell is inverted, as shown in FIG. 3b. Visible artifacts in the displayed image are reduced for certain images in comparison to column inversion. Generally, dot inversion requires increased power consumption in comparison to column inversion.
The aforementioned popular scan driving methods of row inversion, column inversion, and dot inversion have different degrees of sensitivity towards different image data patterns, with regard to visible crosstalk and flicker problems. Row inversion driving is prone to generate visible artifacts for certain horizontal line image data patterns, column inversion driving is prone to generate visible artifacts for certain vertical line image data patterns, and dot inversion driving is prone to generate visible artifacts for certain cell level image date patterns.
Due to such sensitivity to image data patterns, US patent No. 2004/0032386 discloses a time averaging method of voltage polarity patterns for driving LCD. The method comprises a systematic frame by frame row rotation of row divided voltage polarity pattern blocks for the LCD panel, wherein adjacent blocks have opposite column inversion voltage polarity pattern as shown in FIG. 4a, relying on a frame time averaging of the visible effects to reduce overall perceived average of crosstalk and flicker visible artifacts. The polarity pattern comprises polarity inversion from column to column within a polarity pattern block, similar to the case of column inversion, except that polarity is also inverted between polarity pattern blocks.
U.S. Pat. No. 6,335,719 discloses a spatial averaging method of voltage polarity patterns for driving LCD. The method comprises an arrangement of voltage polarity pattern blocks for the LCD panel, wherein adjacent blocks have opposite dot inversion voltage polarity patterns as shown in FIG. 4b, relying on a spatial averaging effect to reduce overall perceived average of crosstalk and flicker visible artifacts. The polarity pattern comprises polarity inversion from column to column and from row to row within a polarity pattern block, similar to the case of dot inversion, except that polarity is also inverted between polarity pattern blocks.
There are other prior arts employing similar time or spatial or a combination of time and spatial averaging schemes, including U.S. Pat. No. 6,332,876, US 2004/0207592, US 2005/0264598, US 2008/0158125, and US 2010/0097367.
The trend is towards high image resolution and large panel size in display applications. High image resolution and large panel size require high speed driving signals, increasing difficulty in achieving consistent signal voltages across LC cells and thus aggravating visible artifacts. Increasingly complicate inversion schemes result in increasingly difficult hardware integration and high power consumption. To meet requirements for high quality image resolution, large LCD panel size, and stringent hardware limitation and power consumption budget, there is a serious need to improve LCD driving method in continual development.